/*
 * ESemaphore.hh
 *
 *  Created on: 2015-2-7
 *      Author: cxxjava@163.com
 */

#ifndef ESEMAPHORE_HH_
#define ESEMAPHORE_HH_

#include "../EString.hh"
#include "../ETimeUnit.hh"
#include "../EThread.hh"
#include "../ECollection.hh"
#include "../EInterruptedException.hh"

# define SEMAPHORE_SYNCBLOCK(lock) { \
	efc::semaphore::Guard __synchronizer__(lock);

namespace efc {
	namespace semaphore {
		class Sync;
	}
}

namespace efc {

/**
 * A counting semaphore.  Conceptually, a semaphore maintains a set of
 * permits.  Each {@link #acquire} blocks if necessary until a permit is
 * available, and then takes it.  Each {@link #release} adds a permit,
 * potentially releasing a blocking acquirer.
 * However, no actual permit objects are used; the {@code Semaphore} just
 * keeps a count of the number available and acts accordingly.
 *
 * <p>Semaphores are often used to restrict the number of threads than can
 * access some (physical or logical) resource. For example, here is
 * a class that uses a semaphore to control access to a pool of items:
 *  <pre> {@code
 * class Pool {
 *   private static final int MAX_AVAILABLE = 100;
 *   private final Semaphore available = new Semaphore(MAX_AVAILABLE, true);
 *
 *   public Object getItem() throws InterruptedException {
 *     available.acquire();
 *     return getNextAvailableItem();
 *   }
 *
 *   public void putItem(Object x) {
 *     if (markAsUnused(x))
 *       available.release();
 *   }
 *
 *   // Not a particularly efficient data structure; just for demo
 *
 *   protected Object[] items = ... whatever kinds of items being managed
 *   protected boolean[] used = new boolean[MAX_AVAILABLE];
 *
 *   protected synchronized Object getNextAvailableItem() {
 *     for (int i = 0; i < MAX_AVAILABLE; ++i) {
 *       if (!used[i]) {
 *          used[i] = true;
 *          return items[i];
 *       }
 *     }
 *     return null; // not reached
 *   }
 *
 *   protected synchronized boolean markAsUnused(Object item) {
 *     for (int i = 0; i < MAX_AVAILABLE; ++i) {
 *       if (item == items[i]) {
 *          if (used[i]) {
 *            used[i] = false;
 *            return true;
 *          } else
 *            return false;
 *       }
 *     }
 *     return false;
 *   }
 * }}</pre>
 *
 * <p>Before obtaining an item each thread must acquire a permit from
 * the semaphore, guaranteeing that an item is available for use. When
 * the thread has finished with the item it is returned back to the
 * pool and a permit is returned to the semaphore, allowing another
 * thread to acquire that item.  Note that no synchronization lock is
 * held when {@link #acquire} is called as that would prevent an item
 * from being returned to the pool.  The semaphore encapsulates the
 * synchronization needed to restrict access to the pool, separately
 * from any synchronization needed to maintain the consistency of the
 * pool itself.
 *
 * <p>A semaphore initialized to one, and which is used such that it
 * only has at most one permit available, can serve as a mutual
 * exclusion lock.  This is more commonly known as a <em>binary
 * semaphore</em>, because it only has two states: one permit
 * available, or zero permits available.  When used in this way, the
 * binary semaphore has the property (unlike many {@link java.util.concurrent.locks.Lock}
 * implementations), that the &quot;lock&quot; can be released by a
 * thread other than the owner (as semaphores have no notion of
 * ownership).  This can be useful in some specialized contexts, such
 * as deadlock recovery.
 *
 * <p> The constructor for this class optionally accepts a
 * <em>fairness</em> parameter. When set false, this class makes no
 * guarantees about the order in which threads acquire permits. In
 * particular, <em>barging</em> is permitted, that is, a thread
 * invoking {@link #acquire} can be allocated a permit ahead of a
 * thread that has been waiting - logically the new thread places itself at
 * the head of the queue of waiting threads. When fairness is set true, the
 * semaphore guarantees that threads invoking any of the {@link
 * #acquire() acquire} methods are selected to obtain permits in the order in
 * which their invocation of those methods was processed
 * (first-in-first-out; FIFO). Note that FIFO ordering necessarily
 * applies to specific internal points of execution within these
 * methods.  So, it is possible for one thread to invoke
 * {@code acquire} before another, but reach the ordering point after
 * the other, and similarly upon return from the method.
 * Also note that the untimed {@link #tryAcquire() tryAcquire} methods do not
 * honor the fairness setting, but will take any permits that are
 * available.
 *
 * <p>Generally, semaphores used to control resource access should be
 * initialized as fair, to ensure that no thread is starved out from
 * accessing a resource. When using semaphores for other kinds of
 * synchronization control, the throughput advantages of non-fair
 * ordering often outweigh fairness considerations.
 *
 * <p>This class also provides convenience methods to {@link
 * #acquire(int) acquire} and {@link #release(int) release} multiple
 * permits at a time.  Beware of the increased risk of indefinite
 * postponement when these methods are used without fairness set true.
 *
 * <p>Memory consistency effects: Actions in a thread prior to calling
 * a "release" method such as {@code release()}
 * <a href="package-summary.html#MemoryVisibility"><i>happen-before</i></a>
 * actions following a successful "acquire" method such as {@code acquire()}
 * in another thread.
 *
 * @since 1.5
 */

class ESemaphore: public EObject {
public:
	virtual ~ESemaphore();

	/**
	 * Creates a {@code Semaphore} with the given number of
	 * permits and nonfair fairness setting.
	 *
	 * @param permits the initial number of permits available.
	 *        This value may be negative, in which case releases
	 *        must occur before any acquires will be granted.
	 */
	ESemaphore(int permits);

	/**
	 * Creates a {@code Semaphore} with the given number of
	 * permits and the given fairness setting.
	 *
	 * @param permits the initial number of permits available.
	 *        This value may be negative, in which case releases
	 *        must occur before any acquires will be granted.
	 * @param fair {@code true} if this semaphore will guarantee
	 *        first-in first-out granting of permits under contention,
	 *        else {@code false}
	 */
	ESemaphore(int permits, boolean fair);

	/**
	 * Acquires a permit from this semaphore, blocking until one is
	 * available, or the thread is {@linkplain Thread#interrupt interrupted}.
	 *
	 * <p>Acquires a permit, if one is available and returns immediately,
	 * reducing the number of available permits by one.
	 *
	 * <p>If no permit is available then the current thread becomes
	 * disabled for thread scheduling purposes and lies dormant until
	 * one of two things happens:
	 * <ul>
	 * <li>Some other thread invokes the {@link #release} method for this
	 * semaphore and the current thread is next to be assigned a permit; or
	 * <li>Some other thread {@linkplain Thread#interrupt interrupts}
	 * the current thread.
	 * </ul>
	 *
	 * <p>If the current thread:
	 * <ul>
	 * <li>has its interrupted status set on entry to this method; or
	 * <li>is {@linkplain Thread#interrupt interrupted} while waiting
	 * for a permit,
	 * </ul>
	 * then {@link InterruptedException} is thrown and the current thread's
	 * interrupted status is cleared.
	 *
	 * @throws InterruptedException if the current thread is interrupted
	 */
	void acquire() THROWS (EInterruptedException);

	/**
	 * Acquires a permit from this semaphore, blocking until one is
	 * available.
	 *
	 * <p>Acquires a permit, if one is available and returns immediately,
	 * reducing the number of available permits by one.
	 *
	 * <p>If no permit is available then the current thread becomes
	 * disabled for thread scheduling purposes and lies dormant until
	 * some other thread invokes the {@link #release} method for this
	 * semaphore and the current thread is next to be assigned a permit.
	 *
	 * <p>If the current thread is {@linkplain Thread#interrupt interrupted}
	 * while waiting for a permit then it will continue to wait, but the
	 * time at which the thread is assigned a permit may change compared to
	 * the time it would have received the permit had no interruption
	 * occurred.  When the thread does return from this method its interrupt
	 * status will be set.
	 */
	void acquireUninterruptibly();

	/**
	 * Acquires a permit from this semaphore, only if one is available at the
	 * time of invocation.
	 *
	 * <p>Acquires a permit, if one is available and returns immediately,
	 * with the value {@code true},
	 * reducing the number of available permits by one.
	 *
	 * <p>If no permit is available then this method will return
	 * immediately with the value {@code false}.
	 *
	 * <p>Even when this semaphore has been set to use a
	 * fair ordering policy, a call to {@code tryAcquire()} <em>will</em>
	 * immediately acquire a permit if one is available, whether or not
	 * other threads are currently waiting.
	 * This &quot;barging&quot; behavior can be useful in certain
	 * circumstances, even though it breaks fairness. If you want to honor
	 * the fairness setting, then use
	 * {@link #tryAcquire(long, TimeUnit) tryAcquire(0, TimeUnit.SECONDS) }
	 * which is almost equivalent (it also detects interruption).
	 *
	 * @return {@code true} if a permit was acquired and {@code false}
	 *         otherwise
	 */
	boolean tryAcquire();

	/**
	 * Acquires a permit from this semaphore, if one becomes available
	 * within the given waiting time and the current thread has not
	 * been {@linkplain Thread#interrupt interrupted}.
	 *
	 * <p>Acquires a permit, if one is available and returns immediately,
	 * with the value {@code true},
	 * reducing the number of available permits by one.
	 *
	 * <p>If no permit is available then the current thread becomes
	 * disabled for thread scheduling purposes and lies dormant until
	 * one of three things happens:
	 * <ul>
	 * <li>Some other thread invokes the {@link #release} method for this
	 * semaphore and the current thread is next to be assigned a permit; or
	 * <li>Some other thread {@linkplain Thread#interrupt interrupts}
	 * the current thread; or
	 * <li>The specified waiting time elapses.
	 * </ul>
	 *
	 * <p>If a permit is acquired then the value {@code true} is returned.
	 *
	 * <p>If the current thread:
	 * <ul>
	 * <li>has its interrupted status set on entry to this method; or
	 * <li>is {@linkplain Thread#interrupt interrupted} while waiting
	 * to acquire a permit,
	 * </ul>
	 * then {@link InterruptedException} is thrown and the current thread's
	 * interrupted status is cleared.
	 *
	 * <p>If the specified waiting time elapses then the value {@code false}
	 * is returned.  If the time is less than or equal to zero, the method
	 * will not wait at all.
	 *
	 * @param timeout the maximum time to wait for a permit
	 * @param unit the time unit of the {@code timeout} argument
	 * @return {@code true} if a permit was acquired and {@code false}
	 *         if the waiting time elapsed before a permit was acquired
	 * @throws InterruptedException if the current thread is interrupted
	 */
	boolean tryAcquire(llong timeout, ETimeUnit *unit) THROWS (EInterruptedException);

	/**
	 * Releases a permit, returning it to the semaphore.
	 *
	 * <p>Releases a permit, increasing the number of available permits by
	 * one.  If any threads are trying to acquire a permit, then one is
	 * selected and given the permit that was just released.  That thread
	 * is (re)enabled for thread scheduling purposes.
	 *
	 * <p>There is no requirement that a thread that releases a permit must
	 * have acquired that permit by calling {@link #acquire}.
	 * Correct usage of a semaphore is established by programming convention
	 * in the application.
	 */
	void release();

	/**
	 * Acquires the given number of permits from this semaphore,
	 * blocking until all are available,
	 * or the thread is {@linkplain Thread#interrupt interrupted}.
	 *
	 * <p>Acquires the given number of permits, if they are available,
	 * and returns immediately, reducing the number of available permits
	 * by the given amount.
	 *
	 * <p>If insufficient permits are available then the current thread becomes
	 * disabled for thread scheduling purposes and lies dormant until
	 * one of two things happens:
	 * <ul>
	 * <li>Some other thread invokes one of the {@link #release() release}
	 * methods for this semaphore, the current thread is next to be assigned
	 * permits and the number of available permits satisfies this request; or
	 * <li>Some other thread {@linkplain Thread#interrupt interrupts}
	 * the current thread.
	 * </ul>
	 *
	 * <p>If the current thread:
	 * <ul>
	 * <li>has its interrupted status set on entry to this method; or
	 * <li>is {@linkplain Thread#interrupt interrupted} while waiting
	 * for a permit,
	 * </ul>
	 * then {@link InterruptedException} is thrown and the current thread's
	 * interrupted status is cleared.
	 * Any permits that were to be assigned to this thread are instead
	 * assigned to other threads trying to acquire permits, as if
	 * permits had been made available by a call to {@link #release()}.
	 *
	 * @param permits the number of permits to acquire
	 * @throws InterruptedException if the current thread is interrupted
	 * @throws IllegalArgumentException if {@code permits} is negative
	 */
	void acquire(int permits) THROWS (EInterruptedException);

	/**
	 * Acquires the given number of permits from this semaphore,
	 * blocking until all are available.
	 *
	 * <p>Acquires the given number of permits, if they are available,
	 * and returns immediately, reducing the number of available permits
	 * by the given amount.
	 *
	 * <p>If insufficient permits are available then the current thread becomes
	 * disabled for thread scheduling purposes and lies dormant until
	 * some other thread invokes one of the {@link #release() release}
	 * methods for this semaphore, the current thread is next to be assigned
	 * permits and the number of available permits satisfies this request.
	 *
	 * <p>If the current thread is {@linkplain Thread#interrupt interrupted}
	 * while waiting for permits then it will continue to wait and its
	 * position in the queue is not affected.  When the thread does return
	 * from this method its interrupt status will be set.
	 *
	 * @param permits the number of permits to acquire
	 * @throws IllegalArgumentException if {@code permits} is negative
	 */
	void acquireUninterruptibly(int permits);

	/**
	 * Acquires the given number of permits from this semaphore, only
	 * if all are available at the time of invocation.
	 *
	 * <p>Acquires the given number of permits, if they are available, and
	 * returns immediately, with the value {@code true},
	 * reducing the number of available permits by the given amount.
	 *
	 * <p>If insufficient permits are available then this method will return
	 * immediately with the value {@code false} and the number of available
	 * permits is unchanged.
	 *
	 * <p>Even when this semaphore has been set to use a fair ordering
	 * policy, a call to {@code tryAcquire} <em>will</em>
	 * immediately acquire a permit if one is available, whether or
	 * not other threads are currently waiting.  This
	 * &quot;barging&quot; behavior can be useful in certain
	 * circumstances, even though it breaks fairness. If you want to
	 * honor the fairness setting, then use {@link #tryAcquire(int,
	 * long, TimeUnit) tryAcquire(permits, 0, TimeUnit.SECONDS) }
	 * which is almost equivalent (it also detects interruption).
	 *
	 * @param permits the number of permits to acquire
	 * @return {@code true} if the permits were acquired and
	 *         {@code false} otherwise
	 * @throws IllegalArgumentException if {@code permits} is negative
	 */
	boolean tryAcquire(int permits);

	/**
	 * Acquires the given number of permits from this semaphore, if all
	 * become available within the given waiting time and the current
	 * thread has not been {@linkplain Thread#interrupt interrupted}.
	 *
	 * <p>Acquires the given number of permits, if they are available and
	 * returns immediately, with the value {@code true},
	 * reducing the number of available permits by the given amount.
	 *
	 * <p>If insufficient permits are available then
	 * the current thread becomes disabled for thread scheduling
	 * purposes and lies dormant until one of three things happens:
	 * <ul>
	 * <li>Some other thread invokes one of the {@link #release() release}
	 * methods for this semaphore, the current thread is next to be assigned
	 * permits and the number of available permits satisfies this request; or
	 * <li>Some other thread {@linkplain Thread#interrupt interrupts}
	 * the current thread; or
	 * <li>The specified waiting time elapses.
	 * </ul>
	 *
	 * <p>If the permits are acquired then the value {@code true} is returned.
	 *
	 * <p>If the current thread:
	 * <ul>
	 * <li>has its interrupted status set on entry to this method; or
	 * <li>is {@linkplain Thread#interrupt interrupted} while waiting
	 * to acquire the permits,
	 * </ul>
	 * then {@link InterruptedException} is thrown and the current thread's
	 * interrupted status is cleared.
	 * Any permits that were to be assigned to this thread, are instead
	 * assigned to other threads trying to acquire permits, as if
	 * the permits had been made available by a call to {@link #release()}.
	 *
	 * <p>If the specified waiting time elapses then the value {@code false}
	 * is returned.  If the time is less than or equal to zero, the method
	 * will not wait at all.  Any permits that were to be assigned to this
	 * thread, are instead assigned to other threads trying to acquire
	 * permits, as if the permits had been made available by a call to
	 * {@link #release()}.
	 *
	 * @param permits the number of permits to acquire
	 * @param timeout the maximum time to wait for the permits
	 * @param unit the time unit of the {@code timeout} argument
	 * @return {@code true} if all permits were acquired and {@code false}
	 *         if the waiting time elapsed before all permits were acquired
	 * @throws InterruptedException if the current thread is interrupted
	 * @throws IllegalArgumentException if {@code permits} is negative
	 */
	boolean tryAcquire(int permits, llong timeout, ETimeUnit *unit) THROWS (EInterruptedException);

	/**
	 * Releases the given number of permits, returning them to the semaphore.
	 *
	 * <p>Releases the given number of permits, increasing the number of
	 * available permits by that amount.
	 * If any threads are trying to acquire permits, then one
	 * is selected and given the permits that were just released.
	 * If the number of available permits satisfies that thread's request
	 * then that thread is (re)enabled for thread scheduling purposes;
	 * otherwise the thread will wait until sufficient permits are available.
	 * If there are still permits available
	 * after this thread's request has been satisfied, then those permits
	 * are assigned in turn to other threads trying to acquire permits.
	 *
	 * <p>There is no requirement that a thread that releases a permit must
	 * have acquired that permit by calling {@link Semaphore#acquire acquire}.
	 * Correct usage of a semaphore is established by programming convention
	 * in the application.
	 *
	 * @param permits the number of permits to release
	 * @throws IllegalArgumentException if {@code permits} is negative
	 */
	void release(int permits);

	/**
	 * Returns the current number of permits available in this semaphore.
	 *
	 * <p>This method is typically used for debugging and testing purposes.
	 *
	 * @return the number of permits available in this semaphore
	 */
	int availablePermits();

	/**
	 * Acquires and returns all permits that are immediately available.
	 *
	 * @return the number of permits acquired
	 */
	int drainPermits();

	/**
	 * Returns {@code true} if this semaphore has fairness set true.
	 *
	 * @return {@code true} if this semaphore has fairness set true
	 */
	boolean isFair();

	/**
	 * Queries whether any threads are waiting to acquire. Note that
	 * because cancellations may occur at any time, a {@code true}
	 * return does not guarantee that any other thread will ever
	 * acquire.  This method is designed primarily for use in
	 * monitoring of the system state.
	 *
	 * @return {@code true} if there may be other threads waiting to
	 *         acquire the lock
	 */
	boolean hasQueuedThreads();

	/**
	 * Returns an estimate of the number of threads waiting to acquire.
	 * The value is only an estimate because the number of threads may
	 * change dynamically while this method traverses internal data
	 * structures.  This method is designed for use in monitoring of the
	 * system state, not for synchronization control.
	 *
	 * @return the estimated number of threads waiting for this lock
	 */
	int getQueueLength();

	/**
	 * Returns a string identifying this semaphore, as well as its state.
	 * The state, in brackets, includes the String {@code "Permits ="}
	 * followed by the number of permits.
	 *
	 * @return a string identifying this semaphore, as well as its state
	 */
	virtual EString toString();

protected:
	/**
	 * Shrinks the number of available permits by the indicated
	 * reduction. This method can be useful in subclasses that use
	 * semaphores to track resources that become unavailable. This
	 * method differs from {@code acquire} in that it does not block
	 * waiting for permits to become available.
	 *
	 * @param reduction the number of permits to remove
	 * @throws IllegalArgumentException if {@code reduction} is negative
	 */
	void reducePermits(int reduction);

	/**
	 * Returns a collection containing threads that may be waiting to acquire.
	 * Because the actual set of threads may change dynamically while
	 * constructing this result, the returned collection is only a best-effort
	 * estimate.  The elements of the returned collection are in no particular
	 * order.  This method is designed to facilitate construction of
	 * subclasses that provide more extensive monitoring facilities.
	 *
	 * @return the collection of threads
	 */
	ECollection<EThread*>* getQueuedThreads();

private:
	semaphore::Sync *sync;
};

namespace semaphore {
	class Guard {
	public:
		Guard(ESemaphore* lock) : _lock(lock) {
			if (_lock) {
				_lock->acquire();
			}
		}
		~Guard() {
			if (_lock) {
				_lock->release();
			}
		}
	private:
		ESemaphore* _lock;
	};
}

} /* namespace efc */
#endif /* ESEMAPHORE_HH_ */
